U.S. patent application number 10/808393 was filed with the patent office on 2005-06-30 for chip carrier used for semiconductor optical device, optical module, and optical transmitter and receiver.
Invention is credited to Arimoto, Hideo, Naoe, Kazuhiko, Sasada, Noriko, Shirai, Masataka, Tada, Satoshi.
Application Number | 20050139843 10/808393 |
Document ID | / |
Family ID | 34697678 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139843 |
Kind Code |
A1 |
Sasada, Noriko ; et
al. |
June 30, 2005 |
Chip carrier used for semiconductor optical device, optical module,
and optical transmitter and receiver
Abstract
A chip carrier includes a metal-coated portion formed on a front
surface of a substrate and to be mounted a device, and a rear
surface of the substrate being coated with a metal, in which a
metal-coated portion is formed on a side surface of the substrate
and the metal-coated portion on the front surface of substrate is
connected with the metal-coated portion on the rear surface by the
metal-coated portion formed on the side surface of the substrate,
thereby maintaining frequency characteristics of the optical
semiconductor device.
Inventors: |
Sasada, Noriko; (Yokohama,
JP) ; Naoe, Kazuhiko; (Yokohama, JP) ; Shirai,
Masataka; (Higashimurayama, JP) ; Arimoto, Hideo;
(Kokubunji, JP) ; Tada, Satoshi; (Chigasaki,
JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
34697678 |
Appl. No.: |
10/808393 |
Filed: |
March 25, 2004 |
Current U.S.
Class: |
257/81 ;
257/82 |
Current CPC
Class: |
H01S 5/0265 20130101;
H01S 5/02325 20210101; G02B 6/4201 20130101; G02B 6/4279 20130101;
H01S 5/06226 20130101; H01L 2224/48091 20130101; H01S 5/0237
20210101; G02B 6/428 20130101; H01S 5/0085 20130101; H01L
2224/48091 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
257/081 ;
257/082 |
International
Class: |
H01L 027/15; H01L
033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2003 |
JP |
2003-432013 |
Claims
What is claimed is:
1. A chip carrier including a metal-coated portion formed on a
front surface of a substrate and to be mounted a device, and a rear
surface of the substrate being coated with a metal, wherein a
metal-coated portion is formed on a side surface of the substrate,
and wherein the metal-coated portion on the front surface of
substrate is connected with the metal-coated portion on the rear
surface by the metal-coated portion formed on the side surface of
the substrate.
2. The chip carrier according to claim 1, wherein the metal-coated
portion on the front surface of the substrate is connected with the
metal-coated portion on the rear surface by a metallic via-hole
formed on passing through the substrate.
3. A chip carrier including a metal-coated portion formed on a
front surface of a substrate and mounted an optical semiconductor
device, and a rear surface of the substrate being coated with a
metal, wherein a metal-coated portion is formed on a side surface
of the substrate, and wherein the metal-coated portion on the front
surface of substrate is connected with the metal-coated portion on
the rear surface by the metal-coated portion formed on the side
surface of the substrate.
4. The chip carrier according to claim 3, wherein the metal-coated
portion on the front surface of the substrate is connected with the
metal-coated portion on the rear surface by a metallic via-hole
formed on passing through the substrate.
5. The chip carrier according to claim 3, wherein the metal-coated
portion formed on the side surface of the substrate is formed on
the side surface closest to a position at which the optical
semiconductor device is mounted.
6. The chip carrier according to claim 5, wherein an area of the
metal-coated portion formed on the side surface of the substrate is
equal to or greater than 1/3 of the side surface.
7. An optical module incorporating a chip carrier with an optical
semiconductor device mounted, wherein the chip carrier including a
substrate, a rear, a front and a side surfaces of the substrate
being coated with a metal, and the optical semiconductor device
being mounted on the metal-coated portion of the front surface, and
wherein the metal-coated portion on the front surface of the
substrate is connected with the metal-coated portion on the rear
surface by the metal-coated portion formed on the side surface of
the substrate.
8. The optical module according to claim 7, wherein the
metal-coated portion on the front surface of the substrate of the
chip carrier is further connected with the metal-coated portion on
the rear surface by a metallic via-hole formed on passing through
the substrate.
9. The optical module according to claim 7, wherein the
metal-coated portion formed on the side surface of the substrate of
the chip carrier is formed on the side surface closest to a
position at which the optical semiconductor device is mounted.
10. The optical module according to claim 9, wherein an area of the
metal-coated portion formed on the side surface of the substrate of
the chip carrier is equal to or greater than 1/3 of the side
surface.
11. A chip carrier including a metal-coated portion formed on a
front surface of a substrate and mounted an optical semiconductor
device, and a rear surface of the substrate being coated with a
metal, wherein the metal-coated portion on the front surface of the
substrate is connected with the metal-coated portion on the rear
surface by a metallic via-hole formed on passing through the
substrate, and wherein the via hole is formed below the optical
semiconductor device.
12. The chip carrier according to claim 11, wherein a metal-coated
portion is formed on a side of the substrate, and wherein the
metal-coated portion on the front surface of the substrate is
further connected with the metal-coated portion on the rear surface
by the metal-coated portion formed on the side surface of the
substrate.
13. An optical module incorporating a chip carrier with an optical
semiconductor device mounted, wherein the chip carrier includes a
substrate, a rear and a front surfaces of which are coated with a
metal, and the optical semiconductor device being mounted on the
metal-coated portion on the front surface, wherein the metal-coated
portion on the front surface of the substrate is connected with the
metal-coated portion on the rear surface by a metallic via-hole
formed on passing through the substrate, and wherein the via-hole
is formed below the optical semiconductor device.
14. The optical module according to claim 13, wherein a
metal-coated portion is formed on a side of the substrate, and
wherein the metal-coated portion on the front surface of the
substrate of the chip carrier is further connected with the
metal-coated portion on the rear surface by the metal-coated
portion formed on the side surface of the substrate.
15. An optical transceiver incorporating an optical module
constituted of chip carriers on which optical semiconductor devices
are mounted, respectively wherein each of the chip carriers for
transmission and reception includes the optical semiconductor
device mounted on a metal-coated portion formed on a front surface
of a substrate, a rear and a side surfaces of which are coated with
a metal, and wherein the metal-coated portion on the front surface
of the substrate is connected with a metal-coated portion on the
rear surface by the metal-coated portion formed on the side surface
of the substrate.
16. An optical transceiver incorporating an optical module
constituted of chip carriers on which optical semiconductor
devices, respectively are mounted, wherein each of the chip
carriers for transmission and reception includes the optical
semiconductor device mounted on a metal-coated portion formed on a
front surface of a substrate, a rear side surface of which is
coated with a metal, wherein the metal-coated portion on the front
surface of the substrate is connected with the metal-coated portion
on the rear surface by a metallic via-hole formed on passing
through the substrate, and wherein the via-hole is formed below the
optical semiconductor device.
Description
[0001] This application relates to Japanese Patent Application No.
2003-432013 filed on Dec. 26, 2003, the entire disclosure of which
is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a chip carrier
incorporating an optical semiconductor device or the like mounted
thereon, an optical module using this chip carrier, and an optical
transceiver.
[0004] 2. Description of the Related Art
[0005] In general, an optical module is formed by incorporating a
chip carrier on which an optical semiconductor device or the like
such as a semiconductor laser diode (hereinafter, referred to as an
LD) is mounted by soldering those onto a package including a power
supply terminal, an input signal terminal, a ground terminal, an
optical output fiber connector terminal and the like. As the chip
carrier, there is used a dielectric material or a semiconductor
substrate. The optical semiconductor device is mounted on a ground
metal-coated portion, by soldering, formed on the surface of the
dielectric material or semiconductor substrate, and the optical
semiconductor device is then connected with a high-frequency
transmission line or the like formed on the same substrate surface
through wire-bonding.
[0006] With increase of operating speed in relation to the optical
semiconductor device in recent years, excellent high-frequency
characteristics have also been demanded with respect to the chip
carrier. As a structural example of the chip carrier aiming at an
improvement in the high-frequency characteristics, JP-A-10-275957
discloses a structure in which a conductive substrate having an
optical semiconductor device mounted thereon is incorporated with a
dielectric material or a semiconductor substrate having a
high-frequency transmission line and a terminating resistor
arranged thereon.
[0007] In an ordinary chip carrier using only a dielectric material
or a semiconductor substrate, excellent characteristics are hard to
be obtained in a high-frequency domain of 20 GHz or above.
[0008] Further, in such a chip carrier in which the conductive
substrate and high-frequency transmission substrate are separately
provided as disclosed in JP-A-10-275957, although high-frequency
characteristics are relatively good, there is a problem that its
manufacturing cost is high because of its structure, and a
packaging process requires much time.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a chip
carrier that is superior in the high-frequency characteristics and
has a low cost, an optical module incorporating this chip carrier
assembled therein, and an optical transceiver.
[0010] To achieve this object, reduction of an inductance on the
chip carrier is a dominant means. That is, a high-frequency
transmission line and a ground metal-coated portion are arranged on
a dielectric material or a semiconductor substrate, a rear surface
of which is coated with a metal; the metal-coated portion on the
front surface are electrically connected with the metal-coated
portion on the rear surface through a metallic via-hole; a part or
all of a side surface of the chip carrier is coated with a metal;
and the metal-coated portion on the front surface of the dielectric
material or the semiconductor substrate is electrically connected
with the metal-coated portion on the rear surface.
[0011] Furthermore, as another means for reducing an inductance of
the chip carrier, the reduction of distance between the optical
semiconductor device mounted on the chip carrier and the via-hole
of the chip carrier is also prevailing means. In the present
invention, when distance between the positions of the optical
semiconductor device and the via-hole is relatively close in
minimum, that is, the via-hole is arranged directly below the
optical semiconductor device.
[0012] Thereby, using the chip carrier according to the present
invention does not deteriorate the frequency characteristics of
optical semiconductor device operating at a high speed.
Furthermore, the chip carrier in low cost, an optical module
incorporating the chip carrier and an optical transceiver are
realized.
[0013] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1A and 1B are plane and side views illustrating a chip
carrier structure according to the present invention;
[0015] FIGS. 2A and 2B are diagrams illustrating characteristics
obtained by the chip carrier according to the present
invention;
[0016] FIG. 3 is a diagram showing an equivalent circuit of the
chip carrier according to the present invention;
[0017] FIG. 4 is a plane view illustrating a chip carrier structure
according to the present invention;
[0018] FIG. 5 is a diagram illustrating characteristics obtained by
the chip carrier according to the present invention;
[0019] FIG. 6 is a diagram illustrating an LD module structure
according to the present invention;
[0020] FIG. 7 is a diagram illustrating characteristics obtained by
the LD module according to the present invention;
[0021] FIG. 8 is a plane view illustrating a chip carrier structure
according to the present invention; and
[0022] FIG. 9 is a diagram illustrating characteristics obtained by
the chip carrier according to the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0023] Embodiments according to the present invention will be
described in detail hereinafter.
Embodiment 1
[0024] FIGS. 1A and 1B show an upper surface and a side surface of
a chip carrier 100 in a first embodiment according to the present
invention. The chip carrier 100 uses a substrate 101 comprising a
dielectric material such as alumina (AlN) or a semiconductor formed
of silicon (Si). The following elements are then formed on the
substrate: a high-frequency transmission line 102; a ground
metal-coated portion 103 on which an optical semiconductor device
is mounted; and a terminating resistor 104. The optical
semiconductor device 110 is soldered on the ground metal-coated
portion 103. In this embodiment, a description will be given on the
assumption that an external modulator integrated laser
incorporating a semiconductor laser 111 and an external modulator
112 is used as the optical semiconductor device 110.
[0025] In this embodiment, the high-frequency transmission line 102
is a micro-strip line, and the ground metal-coated portion 103 is
electrically connected with a metal-coated portion on a rear
surface through a via-hole 105.
[0026] It is noted that reference numeral 106 denotes a lead wire
connected to a direct-current power source; 107, a lead wire
connected the micro-strip line with the external modulator 112; and
108, a lead wire connecting the external modulator 112 with a
high-frequency line connected to the terminating resistor 104.
[0027] In the present invention, a part (120) or all side surfaces
of the substrate 101 is coated with a metal, and a metal-coated
portion 103 on the front surface of the substrate is electrically
connected with a metal-coated portion on the rear surface of the
same in order to enhance the ground. It is noted that coating with
a metal on a side surface 150 placed at a position closest to a
modulator 112 directly concerning a high-frequency operation is
most effective, among four side surfaces 150 to 153 of such a chip
carrier as shown in FIG. 4.
[0028] In order to confirm an effect of the present invention, FIG.
2A shows optical response characteristics obtained by an actual
device mounted on the chip carrier (in a case where the side
surface 150 is entirely coated with a metal) according to this
embodiment. It is noted that the optical response means a ratio of
an output light intensity relative to a high-frequency signal
intensity input to the modulator. For the purpose of comparison,
FIG. 2B shows characteristics obtained when the side surface is not
coated with a metal.
[0029] When the side surface is not coated with a metal (FIG. 2B),
the characteristics are abruptly deteriorated in the vicinity of 35
GHz, and a resonance is also produced. On the contrary, when the
side surface 150 is entirely coated with a metal (FIG. 2A), an
abrupt deterioration in the characteristics and the resonance do
not occur, and the optical response of -3 dB is obtained even in
the vicinity of 40 GHz, realizing the excellent high-frequency
characteristics.
[0030] FIG. 3 shows an equivalent circuit when the external
modulation type laser is mounted on the chip carrier. Here,
reference numeral 301 denotes a characteristics impedance of the
high-frequency transmission line 102, i.e., 50 .OMEGA.; 309, a
resistance Rt of the terminating resistor 104, i.e., 50 .OMEGA.;
302, an inductance L1 of a bonding wire 108; 303, an inductance L2
of a bonding wire 109; 304, an internal resistance Rm of the
modulator 112; 305, a parasite capacitance Cm of the modulator 112;
306, a resistance Rc of the chip carrier 100; 307, a capacitance Cc
of the chip carrier 100; and 308, an inductance Lc of the chip
carrier 100.
[0031] It is noted that a laser 111 of the external modulator
integrated laser is of a direct-current drive type, and the
equivalent circuit of the laser portion can be ignored in analysis
of the high-frequency characteristics. Therefore, FIG. 3 shows only
the modulator portion in the equivalent circuit.
[0032] The abrupt deterioration in characteristics or the resonance
in the vicinity of 35 GHz observed in FIG. 2B is caused by a series
resonance due to the parasite capacitance Cm of the modulator 112
and the inductance Lc of the chip carrier 100. Here, a resonance
frequency fr is given by the following expression. 1 fr = 1 2 Lc
Cm
[0033] In order to improve the characteristics by shifting this
series resonance frequency to the high-frequency side, the parasite
capacitance Cm of the modulator must be reduced or the inductance
Lc of the chip carrier must be decreased. However, the capacitance
reduction of the modulator may possibly occur deterioration in
device characteristics such as a drop in an extinction ratio that
is a ratio of ON/OFF of light beams. Therefore, it can be
considered that the inductance reduction of the chip carrier is
dominant means.
[0034] In the structure of FIG. 1, the inductance Lc of the chip
carrier is reduced by coating with the metal on the side surface of
the chip carrier and enhancing the ground, sufficiently increasing
the series resonance frequency. For this reason, it can be
considered that the excellent optical response characteristics is
obtained without such an abrupt deterioration in characteristics or
a resonance as shown in FIG. 2A.
[0035] It is noted that the characteristics differs depending on
the area of the side surface coated with the metal. FIG. 5 shows a
simulation result of frequency characteristics (transmission
characteristics) when {fraction (1/10)}, 1/5, 1/3, 1/2 and all of a
superficial content of the side surface 150 is coated in cases
where the side surface 150 of the chip carrier which is closest to
the modulator portion 121 is coated with a metal.
[0036] It can be understood from the simulation result of FIG. 5
that the frequency characteristics are improved by increasing a
metal-coated area. In particular, in a domain of 40 GHz or above,
it can be revealed that the characteristics substantially
equivalent to those, when the entire surface is coated with a
metal, can be obtained by setting the metal-coated area to 1/3 or
above.
[0037] FIG. 6 is a structural diagram of an LD module 600
incorporating the chip carrier according to this embodiment. A
high-frequency signal 630 is supplied from the outside to the
optical semiconductor device 110 on the chip carrier 100 through a
relay substrate 602. Likewise, a direct-current power 640 for
driving the optical semiconductor device 110 is supplied through a
relay substrate 603. Laser beams 610 from the optical semiconductor
device 110 are condensed by a condenser lens 601, and transmitted
to an optical transmission fiber 620 connected to the outside.
Moreover, in order to monitor an optical output state of the
optical semiconductor device 110, a monitor photodiode 604 is
mounted.
[0038] FIG. 7 shows optical response characteristics obtained from
an actual device when the side surface of chip carrier 100 is
coated with a metal in the LD module depicted in FIG. 6. It is
noted that the side surface of the optical semiconductor device 110
closest to the modulator 112 is entirely coated with a metal. For a
purpose of comparison, optical response characteristics of the LD
module incorporating a chip carrier, the side surface of which is
not coated with the metal mounted thereon are also shown. It was
ensured from this evaluation result that coating the side surface
of the chip carrier results in an improvement of the optical
response characteristics by approximately 10 GHz.
[0039] As described above, according to this embodiment, simply
coating the side surface of inexpensive conventional chip carrier
constituted of the dielectric material or semiconductor substrate
with the metal can obtain the excellent frequency characteristics
without the abrupt deterioration in the characteristics, and it is
possible to provide the chip carrier which is inexpensive, has easy
operating steps and is superior in frequency characteristics, the
optical module using this chip carrier, and the transceiver.
[0040] It is noted that the description has been given as to the
case using the external modulator integrated laser as the optical
semiconductor device in this embodiment, the same effect can also
be expected even if the direct-modulated laser having no external
modulator is used. In this case, the side surface closest to the
position of chip carrier on which the directed-modulated laser is
mounted is coated with the metal.
[0041] The present invention is not restricted to shapes or
properties of constituent components on the chip carrier. For
example, although the high-frequency transmission line is a
micro-strip line in this embodiment, the respective similar effects
can be demonstrated in case of a line (generally, a line of 50
.OMEGA.) which does not attenuate a high-frequency signal such as a
coplanar line or a grounded coplanar line (coplanar line having a
rear surface of the substrate coated with a metal).
Embodiment 2
[0042] It has been apparent from the foregoing embodiment that
reducing an inductance of the chip carrier is important in order to
improve the high-frequency characteristics of the chip carrier.
Here, there can be considered the reduction of distance between the
modulator 112 of the external modulator integrated laser 110
mounted on the chip carrier and the via-hole of the chip carrier as
another means for reducing the inductance. In order to reduce this
distance to the minimum level, it is good enough to arrange the
via-hole 105A directly below the modulator 112 as shown in FIG. 8.
Reference numerals excluding the via-hole 105A denote structures
identical to those described in conjunction with FIG. 1A.
[0043] FIG. 9 shows a simulation result of frequency
characteristics when the via-hole 105A is arranged directly below
the modulator 112 depicted in FIG. 8. As compared with the example
in which the side surface of chip carrier is coated with the metal
described in conjunction with the first embodiment, it is apparent
that the excellent characteristics that a resonance does not occur
in a high-frequency domain can be obtained.
[0044] However, the flatness of a via-hole portion and the
dielectric material or the semiconductor substrate around this
portion may be deteriorated which results in reducing adhesive
property at the time of soldering the device by arranging the
via-hole directly below the device in some cases. Additionally,
there is possibility that stress may be applied to the optical
semiconductor device due to a different thermal expansion
coefficient between the via-hole portion and the substrate and
thereby the reliability of the device may not be guaranteed.
Therefore, a countermeasure against these deteriorations, e.g.,
reinforcement of soldering is additionally applied according to
needs.
[0045] As described above, according to this embodiment, in the
inexpensive conventional chip carrier comprising the dielectric
material or semiconductor substrate, since the excellent frequency
characteristics without the abrupt deterioration or resonance in
characteristics can be obtained by simply changing the position of
via-hole thereof, it is possible to provide a chip carrier which is
inexpensive, has easy operating steps and is superior in frequency
characteristics, the optical module using this chip carrier, and
the optical transceiver. This embodiment is not restricted to
shapes or properties of constituent components on the chip carrier
like the first embodiment.
[0046] Moreover, a further improvement in the high-frequency
characteristics can be expected by conformation in which the first
embodiment is combined with this embodiment, i.e., coating the side
surface of chip carrier with the metal and providing the via-hole
directly below the optical semiconductor device which is operated
with a high frequency.
[0047] It is noted that the description has been given as to the
example in which the external modulator integrated laser is used as
the optical semiconductor device in this embodiment, but the same
effect can be expected even if a direct-modulated laser having no
external modulator is used. In such a case, the via-hole is
arranged directly below a position of the chip carrier at which the
direct-modulated laser is mounted.
[0048] Although a light emitting device has been described in both
the first embodiment and the second embodiment, the present
invention is not restricted thereto, and it is also effective to a
chip carrier of a detector such as a photo diode (PD) or an
avalanche photo diode (APD), an optical module using this chip
carrier, and a PD receiver.
[0049] It is also effective to an optical transceiver which both
the LD module and the PD module mentioned above are incorporated in
the same package.
[0050] Further, the chip carrier according to the present invention
is not restricted to the optical semiconductor device. An
improvement in high-frequency characteristics can be expected by
using the chip carrier according to the present invention as long
as it is a device in which a factor deteriorating high-frequency
characteristics is caused by a parasite capacitance of the device,
i.e., a capacitive device having a capacitor structure such as a
transistor.
[0051] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *